The present invention relates to electric-current supply devices for traction engines of urban or suburban vehicles, and applies more particularly to current-chopper devices.
In devices of this type, in order to make the electric motors operate either in traction or in braking mode, electromechanical switches such as contactors or static switches such as thyristors are used, the implementation of all these changeover-switching means requiring the use of forced-commutation circuits or, in the case of thyristor circuits, their control being subject to a wait for the current of the thyristors to fall below their hypostatic holding current.
In all cases there is a discontinuity of current, which constitutes a not inconsiderable drawback of the known devices.
The invention aims to create a device for supplying power to electric traction motors which are able to be switched between traction and braking, this device allowing traction-braking changeover switching of series-excitation motors in an entirely static and natural way.
Hence the subject of the invention is a device for supplying electric current to at least one series-excitation motor, characterized in that it includes a chopper comprising a midpoint linked to the rotor of the said motor and to which are connected at least one first controlled static switch which is additionally connected to a voltage source for applying a supply current to the electric motor in traction mode, and at least one second controlled static switch, additionally linked to earth, for closing a circuit for linking with a load for the motor operating in generator mode during braking and reverse-biased diode-type changeover-switching means for respectively allowing the supply current of the motor delivered by the first controlled static switch to pass in a first direction while the latter is conducting, and for allowing the current delivered to the circuit for linking with the load by the motor operating in generator mode to pass in a second direction through the said second controlled static switch when the latter is conducting.
The power supply device according to the invention may further include one or more of the following characteristics, taken in isolation or according to all technically possible combinations:
the said first and second controlled static switches are switches formed by IGBT insulated-gate bipolar transistors, PA1 the common point of the chopper is connected to at least one series-excitation motor mounted in a first branch, including a rotor and a field coil of the said motor and the associated diode-type changeover-switching means and to at least one series-excitation motor mounted in a second branch connected in parallel with the first branch and comprising a rotor and a field coil of the said motor and the associated diode-type changeover-switching means, the load for the said motors operating in generator mode being common to the first and to the second branches, PA1 the diode-type changeover-switching means biased in a first direction comprise a first diode connected between the rotor and the associated field coil of the motor and a second diode connected between the said field coil and earth, the said first and second diodes being biased to conduct the supply current of the said motor delivered by the said first controlled static switch when it is conducting, the second controlled static switch being turned off, PA1 the changeover-switching means with diodes biased in a second direction comprise a third diode connected between the rotor and the associated field coil and a fourth diode interposed between the field coil and the load, the said third and fourth diodes being biased to conduct the braking current delivered by the motor operating in generator mode when the second controlled static switch is conducting, the first controlled static switch being turned off, PA1 the changeover-switching means with diodes biased in a second direction comprise a third diode connected between the rotor of the motor arranged in the said first branch and the field coil of the motor arranged in the said second branch, and a fourth diode interposed between the field coil and the load (40), the said third and fourth diodes being biased to conduct the braking current delivered by the motor operating in generator mode when the second controlled static switch is conducting, the first controlled static switch being turned off, PA1 the chopper includes, connected to its midpoint, several first controlled static switches for applying the power supply current to the said at least one electric motor in traction mode, and the same number of second controlled static switches for closing the circuit for linking with the load for the motor operating in generator mode during braking.